1. Field of the Invention
This invention relates to vapor-deposited metal layers which are protected from damage by the application of an organic layer to its surface. The invention further relates to the process of applying the protective organic layer to the surface of the vapor-deposited metal layer and to the photosensitive articles made with the protected metal layer.
In particular, the present invention relates to the application of an organic layer onto the surface of a vapor deposited metal layer. The metal layer is generally formed on a supporting base by any of the various vapor-depositing techniques. Prior to subjecting the deposited metal layer to any physical treatments or stress likely to damage the continuity of the coating (e.g., rolling, folding, bending, and the like) an organic layer is vapor deposited onto the surface of the metal.
2. Description of the Prior Art
Vapor-deposited layers of metals, particularly those on flexible webs, tend to be soft and easily rubbed off. These defects are particularly unacceptable where such layers are to be used as part of an imaging system consisting of a vapor-deposited metal layer and an overcoated photoresist or photopolymer layer. Marks, scuffs, kinks, or abrasions in the metal layer produce voids or areas in the film which contain no useful image, thus interrupting the faithfulness of the image. These photographic defective areas have been called by various names such as pinholes, cinch marks, scuffs, etc., depending on where and how the abrasion was produced. In order to avoid such defects, a protective resin layer is generally coated on the metal layer. This is often done in a separate coating operation on a different coating machine. The difficulty with this practice, however, is that the unprotected vapor-coated metal film must be wound after the vapor-coating operation to transport the material to the more conventional resin coater. Defects such as cinch marks, abrasions, and kinks are often produced during this winding operation.
In order to avoid the problems described above, several attempts have been made to vapor-deposite the metallic and organic layers in the same vaccum chamber, thus eliminating the need to wind the film in a roll between coating operations. One such process is described in U.S. Pat. No. 4,268,541. Here the vapor-deposition chamber is divided into 2 sections, by means of a partition, thereby separating the metal deposition area from the organic deposition section. Thus the organic protective layer is deposited over the metal layer without the need to rewind the roll in between the two coating operations.
The organic compounds used in U.S. Pat. No. 4,268,541 include polymers (for example, those derived from methacrylic acid and acrylic acid), low molecular weight organic compounds containing a carboxyl group (e.g., compounds such as abietic acid, isophthalic acid, behenic acid, terephthalic acid, phthalic acid, etc., and a few random compounds (e.g., Rhodamine B, rosin, a phthalocyanine, a monosaccharide, and an oligosaccharide).
The technique and materials described in U.S. Pat. No. 4,268,541 have been found to be suitable for only limited uses. The layer thickness of 30-600 nm specified is not suitable for many imaging film constructions, and for many processing techniques. In particular, the friction properties of the coating cause layers of the coated material which are stacked or rolled to slide and move out of register. In rolled form, telescoping of the roll is quite serious. This can cause serious delays and expense in further use of the film.
Organic protection layers located between the metal layer and a photoresist layer can drastically affect the oxidizing or etching step and the quality of the resulting image. For, example, excessive thickness of such layers may provide a preferential pathway for the developer or etch solution thereby resulting in image degradation or fine detail loss. This is especially true of material whose final designation is copy or contact reprographic work. Films such as these, called lith or contact films, depend on fine dot arrays to reproduce image tone. Fine dots (3-5%) may be undercut and etched away thereby degrading the quality of the reproduction.
The relatively thick layer of some acid-containing protective materials such as disclosed in U.S. Pat. No. 4,268,541 can also interfere with the etching of the metal by neutralizing the alkaline metal etching solution. Such neutralization inhibits the formation of an etched metal image and thus interferes with the formation of an image of acceptable quality.
Another attempt at overcoming the abrasion problems is described in Japanese patent publication number 56/9736. In this case, the metal and the organic compound are deliberately coated as a single layer; i.e., the metal and organic vapors are substantially mixed in the vapor stream before they are deposited on the support. This is not completely satisfactory because the heated metal vapor can carbonize or decompose the organic material resulting in an unacceptable product. Also, the thickness of the layer is required to be at least 20 to 1000 mm. The scope of organic materials is also quite specific and generally emphasizes organic acid materials.